Furnace



Patented Aug. 25, 1931 UNITED STATES CHARLES LADD Nou'roN, JR., or BOSTON, MASSACHUSETTS FURNACE Application filed February 8, 1929. Serial No. 338,567,

Chemical and physical laboratories, smallscale metallurgical operations, often require furnaces capable of developing and mainl taining high temperatures. Small electric furnaces supply this requirement, but are wasteful of heat and costly to operate in proportion to the thermal values obtained; gas heated furnaces of the general type indicated are capable of developing and mainl taining high temperatures, ofthe orderof 2500D F. only when operated by blowpipe burners by which such temperatures can be maintained only with difiiculty and with large liability to failure.

One factor of ditliculty is the large surface of the furnace chamber itself as'compared with the volume thereof. Thermal energy developed in the small volume of the chamber is dissipated by conduction throughthe Walls of the chamber, especially as the conductivity of the Wall-material rises with temperature-diderential, and by the successively rapid translation of hot vgases through and out of the furnace. Other factors of diiiiculty and detriment are the inability of furnace wall-material to endure stresses due to local expansions and confractions.Y The objects of my invention are, to provide a furnace-structure of'small volumetric capacity. adapted to the purposes above indicated. in Which, with an ordinary Bunsen type burner, temperatures as high as 26000 F. can be quickly attained and economically maintained with the burner operating under normal draft` and which can provide maintained temperatur-es between 28500 and 31009711, if the burner be worked under forced draft.

These objects I have attained bv the smallfurnace structure which exemplifies my invention, in which the material of the furnace Wall is composed of such material. and has such a minutely divided and distributed cellstructure that its coefficient of conductivity at i2000O F. is of the order of 3.1 (B. t. u., oer square foot, per inch thickness. per degree F. temperature diderential, per hour). In general outlines, a small-capacity furnace exemnlifying my invention is illustrated in the drawings hereto annexed, in which Fig. l shows such a furnace in vertical mid-section g Fig. 2, the furnace'chamber block, in top plan View; Y

Fig. 3 shows an alternative form of fur- 55 nace body, in vertical mid-section;

gig. 4: shows a top plan view of the same; an Y Fig. 5 Shows, in vertical mid-section, a modified form.

The body-portion, l, ofthe furnace, here shown, consists of al refractory, llowconductivity block of brick materiahcharacterized by cellular structure. The external shape of this block may be as desired, the'65 cylindrical form shown is compact and convement.

The furnace chamber is formed in this block preferably by boring it out of an originally plane-ended shape.

Thus, I take a preformed cylindrical block 1, of such refractory cellular brick material and, with a boring tool bore the main chamber 2, down to a ledge 3, which will serve to support a refractory-material ring `10, for holding a Crucible` or the like, shown in dotted lines at 1l. From the ledge 3, a sma1ler and conical or conoidal tool is used to make a tapering bore down to the point 4, from which a straight cylindrical hole 5 is bored through the lower surface of the block.

To cover the furnace block, I provide a block 7 of similar material, centrally bored into its bodv at 8, and transversely bored at 9. A ldraught-stack of suitable height will preferably be provided to maintain upward draught from the lpassages in the cover block.

The aperturel 5 in the furnace block is of such diameter asto admit the' delivery end of a Bumsen type gas burner, preferably leavin an annular space between the burner tube and the wal] of the aperture 5, for dinission of auxiliary air to the burner .ame

In Figs. 3 and 4, there is illustrated an al- 95 ternative form of furnace body, in this case made of two blocks of refractoryinsulating material, la, la, which meet at 1"; the furnace chamber -is bored half in one block. and half in the other, the parts 2a, 2a; 3a, 3a; 4, 4", and me CFL cover in a vent 23, which should be connect Y ed to a suitable stack.

5 Whether this, or the cover form shown in Fig. 1, be used, thearrangement is such that, withrespct to the Crucible or other object, K11, to be heated, the furnace chamber is on all sides closed against free radiation to the 0 outside of the apparatus.

' As to thev structure ofthe furnace-block itself: This is of refractory material, containing in its total volume as large a proportion of cellular voids asis consistent with mechanical strength, these voids of small dimensions,y uniform in dimension and uniformly distributed. This type of structure 'a'ordshigh heat insulating properties to the block as a whole, and this property is importantfforthe' purposes of this invention.

especially at kand near the walls ofthe furnace cavity; because there, high insulating value operates to maintainhigh surface temperature. n

i The material' which I have found best adapted to secure these results is kaolin bricln'made byfrothing a mixture of ground kaolin, someV ground kaolin greg, wood flour,

'and water, either by beating it mechanically 'er blowing; air into it, depositing the froth Iwhen freshly madefinto, a mold, filtering' off surplus vvvfater immediately, withattendant shrinkage of the froth, thus stiifening the walls of the air bubbles, initially nucle- Q ated on' 1the wood flour so that the froth becomes 'stable and its bubbles no longer break; then drying, and? afterward burning the brick shapes under regulated conditions 'which include maintenance of a reducing atmosphere in the kiln which prevents too rapid increase ofA temperature which would oc- 'cur lif theconditions permitted the included wood flour to` burn, retarding the rate of .temperature increase within the rangeA where in -kaloin-included water is driven off, and finally: allowing the wood` flour residues t0 burnout in `an oxidizing atmosphere; and lastly-,allowing the brick to cool slowly. The product isl a heat-r`efractory brick which preserves in vits permanent form the froth-strueture of the fluidstarting-material the volume of the brickas a whole `consists largely of minute voidslor cells, all substantially ofthe :sa-meerder of magnitude, uniformly distrib- 6.5 ,utedthe'solid material of the brick is dis- "J: L f

,burnedbrick material surrounding the voids are consequently very thin and therefore offer small areas to heat transmission, and

, moreover impart capacity for interna-l yielding and accommodation to stresses produced by temperature differentials,and therefore the brick are not liable to rupture.

. The conductivity coeiiicient of such brick is graded from theorder of 1.5 B. t. u. per square foot area, per oneinch thickness, per 1O F., per hour,at 400o F., to the order vof 3.0 B. t. u. per square foot area, per one inch thickness, per 1O F., per hour, at 2000o F.

A furnace made as above described operates as follows: The crucible, 10, or other Aobject torbe heated, being placed in the chamber 2, and the coverfblock 7 laid over the furnace block, the blocks being placed on any suitable stand or support (not shown in the drawings), an ignited Bunsen type burner is inserted in the lower opening` in the furnace block. The burning Vgas mixture presently raises the temperature of the surface of brick material on the surface of the chamber wall to incandescence; the high, heat-insulating property ef the cellular structure immediately back of the exposed chamberwall enables the gas flame tobring the vsurface to such temperature. Thereupon the action of the surface of solid incandescent material on the mixture of unconsumed combustible gas and auxiliary air supplied through the annular clearance around the tip of the burner 6, establishes vigorous combustion, accelera-tes the temperature rise in the chamber and maintains it accordingly. Vith a Bunsenv type burner operating under its normal draft, the temperature in a small furnace of this character.quickly'attains and continues at26000 F. Forced draft, putting the burns er inblowpipe action will raise this temperature to the neighborhood of 31000 F". In either condition of draft, the gas consumption -is economical. Under normal burner draft, the furnace operates almost noiselessly. So far as' l aminformed,"temperatures of the stated order have not been attainable in furnaces of the'class designated, except in those of the electrically Vheated type, which are ofhigh first cost, and relatively costly to operate. i i

Sinee'furnaces of the type designated are universally, used to operate on fusible materials of relatively high heat conductivity and are therefore contained in crucibles which, though necessarily refractory, are of as high termal conductivity as is practicable, any object to be heated in such furnace as embodies the above described improved characteristics, will absorb heat into its body and rise in temperature much more slowly than the surface of the furnace chamber wall of my above described improved furnace. Stated conversely: The surface of the furnace chamber wall will rise in temperature, from initiation of combustion to the point of equilibrium, well above 2000 F., far more rapidly than the surface of the object to be heated; consequently the attainment by such object of the tempera-ture at which equilibrium is reached is very rapid, and the temperature of equilibrium very high, materially higher than has heretofore been attainable in gas-furnaces under like conditions of combustion.

As to durability, a. furnace constructed according to these specifications has without injury endured one hundred and more successive heats, under the high temperatures above stated, whereas furnaces of the small-dimensioned type heretofore made or obtainable, are seriously deteriorated or destroyed after not morethan twenty (and usually much fewer) heats to the highest temperatures ob-y tainable in them, which are substantially lower than those obtainable in the improved furnace herein described.

I claim:

l. A fuel fired furnace comprising upper and lower blocks of refractory material, the lower block having a substantially vertical passage diverging upwardly from a point adjacent the lower end thereof to an enlarged portion providing a working chamber in the upper end of the passage, the upper block being adapted to rest on the lower block and having a passage providing a flue extending from the working chamber through this upper Block to the atmosphere, this upper block having refractory material spanning the upper end of the working chamber for retaining heat therein.

2. A fuel fired furnace comprising separable upper and lower blocks of refractory material, the lower block having a substantially vertical passage extending therethrough, this passage diverging upwardly from a point adjacent the lower end thereof to an enlarged portion forming a working chamber at the upper end of the passage, the upper block being adapted to rest on the lower block and to extend across the upper end of the working chamber, this upper block having a substantially horizontal passage extending therethrough and having an opening from its under side to this passage, this opening being smaller than the upper end ofthe working chamber so that refractory material about the opening may overlie the working chamber for retaining heat therein when the material, the lower block having a substan- Y tially vertical passage extending theref through, this passage diverging upwardly from a point adjacent the lower end thereof to an enlarged portion forming a working chamber at the upper end of the passage, the upper block bein-g adapted to rest on the lower block and to extend across the upper end of the working chamber, this upper block having passages extending from the working chamber outwardly away from each other and then inwardly toward each other, and coming together substantially at the upper surface of the upper block to provide a flue for escape of gases from the working chamber, the refractory material between the pa,"- sages forming a bridgepiece extending across the upper end of the working chamber for retaining heat in the latter and for avoiding radiation losses.

4. A fuel fired furnace comprising upperl and lower blocks of refractory material, the lower block having a substantially vertical passage diverging upwardly from a point adjacent the lower end thereof to an enlarged portion providing a working chamber in the upper end of the passage, the upper block being adapted to rest on the lower block and having a passage providing a flue extending from the working chamber through this upper block to the atmosphere, this upper block having refractory material spanning the upper end of the working chamber for retaining heat therein, the material forming the working chamber wall being of low thermal conductivity havingvoids separated by thin membranes, the surface membranes of the chamber becoming almost instantaneously radiant upon heating whereby heat input is rendered substantially immediately available. as usable radiant heat in the furnace chamber.

'l Signed by me at Boston, Massachusetts this fifth day of February 1929.

' CHARLES L. NORTUN, JR. 

